This invention relates to a novel tertiary alcohol compound useful as a monomer to form a polymer which serves as a base resin in chemically amplified resist compositions for microfabrication.
While a number of recent efforts are being made to achieve a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, deep-ultraviolet lithography is thought to hold particular promise as the next generation in microfabrication technology. In particular, photolithography using a KrF or ArF excimer laser as the light source is strongly desired to reach the practical level as the micropatterning technique capable of achieving a feature size of 0.3 xcexcm or less.
The resist materials for use in photolithography using light of an excimer laser, especially ArF excimer laser having a wavelength of 193 nm, are, of course, required to have a high transmittance to light of that wavelength. In addition, they are required to have an etching resistance sufficient to allow for film thickness reduction, a high sensitivity sufficient to eliminate any extra burden on the expensive optical material, and especially, a high resolution sufficient to form a precise micropattern. To meet these requirements, it is crucial to develop a base resin having a high transparency, rigidity and reactivity. None of the currently available polymers satisfy all of these requirements. Practically acceptable resist materials are not yet available.
Known high transparency resins include copolymers of acrylic or methacrylic acid derivatives and polymers containing in the backbone an alicyclic compound derived from a norbornene derivative. All these resins are unsatisfactory. For example, copolymers of acrylic or methacrylic acid derivatives are relatively easy to increase reactivity in that highly reactive monomers can be introduced and acid labile units can be increased as desired, but difficult to increase rigidity because of their backbone structure. On the other hand, the polymers containing an alicyclic compound in the backbone have rigidity within the acceptable range, but are less reactive with acid than poly(meth)acrylate because of their backbone structure, and difficult to increase reactivity because of the low freedom of polymerization. Additionally, since the backbone is highly hydrophobic, these polymers are less adherent when applied to substrates. Therefore, some resist compositions which are formulated using these polymers as the base resin fail to withstand etching although they have satisfactory sensitivity and resolution. Some other resist compositions are highly resistant to etching, but have low sensitivity and low resolution below the practically acceptable level.
An object of the invention is to provide a novel tertiary alcohol compound useful as a monomer to form a polymer for use in the formulation of a photoresist composition which exhibits a high transparency and substrate affinity when processed by photolithography using light with a wavelength of less than 300 nm, especially ArF excimer laser light as the light source.
The inventor has found that a tertiary alcohol compound of formula (1) can be prepared in high yields by a simple method to be described later, that a polymer obtained from this alcohol compound has high transparency at the exposure wavelength of an excimer laser, and that a resist composition comprising the polymer as a base resin is improved in resolution and substrate adhesion.
The invention provides a tertiary alcohol compound having the following general formula (1). 
Herein R1 and R2 are independently a straight, branched or cyclic alkyl group of 1 to 10 carbon atoms in which some or all of the hydrogen atoms on constituent carbon atoms may be substituted with halogen atoms, or R1 and R2, taken together, may form an aliphatic hydrocarbon ring, Y and Z are independently a single bond or a straight, branched or cyclic divalent organic group of 1 to 10 carbon atoms, and k is 0 or 1.
The preferred tertiary alcohol compounds have the following general formula (2). 
Herein R3 and R4 are independently a straight, branched or cyclic alkyl group of 1 to 6 carbon atoms.